1. Field of the Invention
The present invention relates to polyurethane covered rolls for use in various industrial applications such as papermaking, steel making and textile manufacturing. More specifically, this invention is directed to thermally conductive base layers for the polyurethane covering of these industrial rolls, the thermally conductive base layer functioning as a reinforcing layer and, additionally, providing a means for dissipating the heat generated in the polyurethane covering, the heat generation a result of energy loss due to elastic deformation of the roll cover during operation.
2. Description of the Prior Art
Roll coverings fabricated from polymeric or elastomeric materials are used for a wide variety of reasons in many industries. Generally speaking, roll covers perform one or more of the following functions:
1. Support, carry, drive, draw or brake product passing through the nip.
2. Remove or extract liquid from the product passing through the nip.
3. Impregnate or coat product passing through the nip.
4. Calendar or iron product passing through the nip.
5. Texture, emboss, print or imprint a pattern to the product passing through the nip.
6. Laminate layers of product or dissimilar layers of products passing through the nip.
7. Provide protection against corrosion.
The use of polymeric or elastomeric covered rolls adapted for use at high speeds of rotation and under heavy loads or pressures has become increasingly significant in recent years. Of particular interest and significance has been the polyurethane roll cover. The polyurethane roll cover provides excellent load bearing and extraction characteristics, high abrasion and wear resistance with better dynamic performance characteristics as compared to the more conventional elastomeric roll covers (chloroprene, styrene-butadiene, polyisoprene, acrylonitrile-butadiene, etc.)
Among the roll types currently in use are those comprising a rigid metallic structural member called a roll core designed to carry the applied load with a minimum amount of deflection. A resilient covering is sometimes bonded directly to the roll core. In many cases, a base layer and/or an intermediate layer is bonded to the roll core and the resilient roll cover is then bonded to the base or intermediate layer. The process can either be a one-step or two-step process. The base or intermediate layer may be a harder material similar to the cover or it may be made up of a fibrous reinforcing material impregnated with a thermosetting resin. The elastomeric or polymeric covering may be materials such as polyurethane, polyisoprene, chloroprene, styrene-butadiene, acrylonitrile butadiene and the like.
It is also known to utilize internally cooled calendering rolls. U.S. Pat. No. 4,256,034 to Kusters, issuing on Mar. 17, 1983, discloses a paper calendering apparatus comprising a pair of interacting calendering rolls, one of which includes a polyurethane covering. The polyurethane-covered roll additionally comprises means for internally cooling the roll in order to maintain the roll cover temperature below a certain minimum temperature. The Kusters' roll applies a cross-linked polyurethane covering directly to the metal core, there being no intermediate reinforcing member.
U.S. Pat. No. 3,082,683 to Justus, issuing on Mar. 26, 1963, directed attention to the problems associated with heat developed within the rubber coverings which could not be sufficiently dissipated by internal cooling of the roll core. The disclosed solution comprised creating a covering containing a plurality of coolant circulation paths for dissipating the heat developed during deformation of the covering. The elastomeric covering is applied directly to the roll core and the system involves a complicated apparatus for manifolding coolant to the axial coolant passages and recirculating the coolant through a heat exchanger.
Hess, U.S. Pat. No. 3,395,636, discloses the use of a dispersion of finely divided carbon particles distributed throughout the elastomeric covering of a processing roll consisting of an elastomeric covering and a hollow roll core of steel, cast iron or bronze. The elastomeric covering is applied directly to the metal roll core, there being no intermediate resin layer. The only material suggested by Hess for heat dissipation is finely divided carbon particles having a mean diameter particle size in the range of 10 to 40 millimicrons. Additionally, no mention of polyurethane as the elastomeric covering is included in the disclosure.